1. Field of the Invention
The present invention relates to a portable dryer, and more particularly, to a multiple-setting portable dryer and related circuit designs.
2. Description of the Prior Art
The conventional dryer is operable only after establishing connection with an AC power plug through a power cord. The use of the dryer is then limited by the length of the cord to the area that can be reached by the cord from the AC power receptacle. Therefore, it is very inconvenient for traveling purposes, in particular, when traveling in countries where the AC power specifications, such as voltages, cycles, and receptacles vary from one to another. Different converters and transformers are needed if the user wants to use a conventional dryer. Furthermore, since the conventional AC powered dryers are powered by AC currents with sinusoidal amplitudes, most use a diode to control the generation of heat. When the switch is shifted to low heat, the one-way conduction property of the diode filters out a half cycle of the AC current that passes through the heating filament. When the switch is shifted to high heat, the current to the heating filament does not go through the diode so that heat can be generated in full output. At the same time, in order to provide a DC current to the motor, an additional bridge rectifier has to be employed to supply the needed DC power.
A typical portable dryer is disclosed in U.S. Pat. No. 6,327,428, which is incorporated herein by reference. The portable dryer comprises a plurality of heating filaments for generating different levels of heat. A motor of the portable dryer is capable of running at different speeds so that a fan of the portable dryer can blow different volumes of air and heat for the convenience of the user.